KASAN: slab-out-of-bounds Read in bpf_prog_create

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 2015a28f Add linux-next specific files for 20190915
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11880d69600000
kernel config: https://syzkaller.appspot.com/x/.config?x=110691c2286b679a
dashboard link: https://syzkaller.appspot.com/bug?extid=eb853b51b10f1befa0b7
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127c3481600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1150a70d600000

The bug was bisected to:

commit 2f4fa2db75e26995709043c8d3de4632ebed5c4b
Author: Al Viro <vi...@zeniv.linux.org.uk>
Date: Thu Apr 18 03:48:01 2019 +0000

compat_ioctl: unify copy-in of ppp filters

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=145eee1d600000
final crash: https://syzkaller.appspot.com/x/report.txt?x=165eee1d600000
console output: https://syzkaller.appspot.com/x/log.txt?x=125eee1d600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+eb853b...@syzkaller.appspotmail.com
Fixes: 2f4fa2db75e2 ("compat_ioctl: unify copy-in of ppp filters")

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:404 [inline]
BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0xe9/0x250
net/core/filter.c:1351
Read of size 32768 at addr ffff88809cf74000 by task syz-executor183/8575

CPU: 0 PID: 8575 Comm: syz-executor183 Not tainted 5.3.0-rc8-next-20190915
#0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:634
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
memcpy+0x24/0x50 mm/kasan/common.c:122
memcpy include/linux/string.h:404 [inline]
bpf_prog_create+0xe9/0x250 net/core/filter.c:1351
get_filter.isra.0+0x108/0x1a0 drivers/net/ppp/ppp_generic.c:572
ppp_get_filter drivers/net/ppp/ppp_generic.c:584 [inline]
ppp_ioctl+0x129d/0x2590 drivers/net/ppp/ppp_generic.c:801
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:539 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
__do_sys_ioctl fs/ioctl.c:750 [inline]
__se_sys_ioctl fs/ioctl.c:748 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4401a9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffebb37d0a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004401a9
RDX: 00000000200000c0 RSI: 0000000040107447 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401a30
R13: 0000000000401ac0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 8575:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc mm/kasan/common.c:510 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524
__do_kmalloc mm/slab.c:3655 [inline]
__kmalloc_track_caller+0x15f/0x760 mm/slab.c:3670
memdup_user+0x26/0xb0 mm/util.c:172
get_filter.isra.0+0xd7/0x1a0 drivers/net/ppp/ppp_generic.c:568
ppp_get_filter drivers/net/ppp/ppp_generic.c:584 [inline]
ppp_ioctl+0x129d/0x2590 drivers/net/ppp/ppp_generic.c:801
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:539 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
__do_sys_ioctl fs/ioctl.c:750 [inline]
__se_sys_ioctl fs/ioctl.c:748 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff88809cf74000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 0 bytes inside of
4096-byte region [ffff88809cf74000, ffff88809cf75000)
The buggy address belongs to the page:
page:ffffea000273dd00 refcount:1 mapcount:0 mapping:ffff8880aa402000
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0002672988 ffffea00027e7788 ffff8880aa402000
raw: 0000000000000000 ffff88809cf74000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809cf74f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88809cf74f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff88809cf75000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88809cf75080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88809cf75100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Eric Biggers]

Arnd and Al,

This is a correct bisection. This commit needs:

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 267fe2c58087..f55d7937d6c5 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -564,8 +564,9 @@ static struct bpf_prog *get_filter(struct sock_fprog *uprog)
return NULL;

/* uprog->len is unsigned short, so no overflow here */
- fprog.len = uprog->len * sizeof(struct sock_filter);
- fprog.filter = memdup_user(uprog->filter, fprog.len);
+ fprog.len = uprog->len;
+ fprog.filter = memdup_user(uprog->filter,
+ uprog->len * sizeof(struct sock_filter));
if (IS_ERR(fprog.filter))
return ERR_CAST(fprog.filter);

[Eric Biggers]

Arnd and Al,

Why did you ignore this and merge the buggy commit to mainline anyway?
I even told you how to fix it...

- Eric

[Eric Biggers]

From: Eric Biggers <ebig...@google.com>

sock_fprog_kern::len is in units of struct sock_filter, not bytes.

Fixes: 3e859adf3643 ("compat_ioctl: unify copy-in of ppp filters")
Reported-by: syzbot+eb853b...@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebig...@google.com>
---
drivers/net/ppp/ppp_generic.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 0cb1c2d0a8bc..3bf8a8b42983 100644

--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -564,8 +564,9 @@ static struct bpf_prog *get_filter(struct sock_fprog *uprog)
return NULL;

/* uprog->len is unsigned short, so no overflow here */
- fprog.len = uprog->len * sizeof(struct sock_filter);
- fprog.filter = memdup_user(uprog->filter, fprog.len);
+ fprog.len = uprog->len;
+ fprog.filter = memdup_user(uprog->filter,
+ uprog->len * sizeof(struct sock_filter));
if (IS_ERR(fprog.filter))
return ERR_CAST(fprog.filter);

--
2.24.0

[Arnd Bergmann]

On Thu, Dec 5, 2019 at 6:55 AM Eric Biggers <ebig...@kernel.org> wrote:
>
> From: Eric Biggers <ebig...@google.com>
>
> sock_fprog_kern::len is in units of struct sock_filter, not bytes.
>
> Fixes: 3e859adf3643 ("compat_ioctl: unify copy-in of ppp filters")
> Reported-by: syzbot+eb853b...@syzkaller.appspotmail.com
> Signed-off-by: Eric Biggers <ebig...@google.com>

Reviewed-by: Arnd Bergmann <ar...@arndb.de>

Thanks for fixing the bug I introduced!

[Arnd Bergmann]

On Thu, Dec 5, 2019 at 6:22 AM Eric Biggers <ebig...@kernel.org> wrote:

> >
>
> Why did you ignore this and merge the buggy commit to mainline anyway?
> I even told you how to fix it...

I'm sorry about this, I completely missed the email about it originally.

Arnd

[David Miller]

From: Eric Biggers <ebig...@kernel.org>
Date: Wed, 4 Dec 2019 21:54:19 -0800

> From: Eric Biggers <ebig...@google.com>
>
> sock_fprog_kern::len is in units of struct sock_filter, not bytes.
>
> Fixes: 3e859adf3643 ("compat_ioctl: unify copy-in of ppp filters")
> Reported-by: syzbot+eb853b...@syzkaller.appspotmail.com
> Signed-off-by: Eric Biggers <ebig...@google.com>

Applied, thank you.